First, here are some background news stories:
Matt Levine at Bloomberg, in December: The 'Flash Boys' Exchange Is Still Controversial
Robin Wigglesworth at the FT, this month: ‘Flash Boys’ trading venue application triggers backlash
"The Investors’ Exchange, a trading venue made famous by Michael Lewis’ Flash Boys book on high-frequency trading, has applied for full stock market status. But the application has triggered a deluge of responses and fanned the debate about the very nature of the US equity markets...."
And here is the SEC's comment page, a sort of flash mob exchange about markets and market design.
Guide to the perplexed: I like Eric Budish's comment, here: #371 … http://www.sec.gov/comments/10-222/10222-371.pdf.
"For pro-IEX letters, the best place to start is the detailed letters from IEX itself. The letter from Healthy Markets is also very good on details. The letters from Southeastern Asset Management (co-signed by many other asset managers) and from Norges Bank (Norway’s sovereign wealth fund) are a bit shorter but give a sense of how pro-IEX asset managers see the debate.
You can search the comments, e.g. for "IEX" or "Goldman Sachs," etc. to find them...